There is a minimum number of twenty. Characters, so you don't just reply like "cool". Instead, with the twenty characters, you will be forced to reply something like "that's cool because blahbkahblah etc". The 20 character rule helps make people be decriptive and more helpful.

To beat the 20 character rule, you could type,"Hi <.kdkdori" but with no period between the < and the letters.